CODEWITHSUNDEEP
c++
Ivan
Ivan

Reputation: 619

define class as a function returning a reference

I am trying to compile some old source code from another person in my lab. And I cannot really understand the idea of the following trick. Why somebody wants to access CLog2Factory class trough the reference given by gLogFactory()? And how can I successfully compile and link the code below?

The whole code is big, so I made a short example. Keep friend and virtual as they present in original code.
test.h:

class CLog2;

class CLog2Factory
{
    friend class CLog2;
public:
    CLog2Factory() {}
    virtual int init() = 0;
};

CLog2Factory&   gLogFactory();

class CLog2
{
public:
    CLog2() : gLogFactory().init()
        { }
};

test.cpp:

#include "test.h"

int main(int argc, char *argv[])
{
    CLog2 log;

    return 0;
}

I get the following error:

test.h: In constructor ‘CLog2::CLog2()’: test.h:50:15: error: class ‘CLog2’ does not have any field named ‘gLogFactory’
     CLog2() : gLogFactory().init()
               ^ 
test.h:50:28: error: expected ‘{’ before ‘.’ token
         CLog2() : gLogFactory().init()

In fact, I could compile the original code (perhaps I am missing something in my test example). but couldn't link it. Error from linking of original code is the following(file test.h is changed to Log2.h now):

Log2.h:254: undefined reference to `gLogFactory()'

Upvotes: 0

Views: 164

Answers (1)

quantdev
quantdev

Reputation: 23793

Your code is missing something from the original : a member (which as the type returned by the init() method) is initialized by this initialization list, something like :

class CLog2
{
public:
    CLog2() : x(gLogFactory().init())
        { }

    int x;
};

Upvotes: 2

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